Vesnina, who had beaten Williams in their only previous meeting at Wimbledon last year, won the first set and was up a break early in the second set before Williams fought back, taking the middle set in 63 minutes. But Vesnina regrouped to close the former World No.1 out in the third set, 62 57 62.

"At the beginning of the match I was a little bit nervous, even though I've been on the tour for many years," Li said. "I'm happy I could come back and win tonight. Thanks to the fans for supporting me!"

Li is a very popular figure in Cincinnati, having conquered the Premier-level stop a year ago.

"I'm always excited to come back to the Western & Southern Open," she said in her on-court interview. "I always have good memories here and there's not much else to say, other than the fans are great."

In an all-unseeded match-up, Magdalena Rybarikova kept her sizzling summer going with a 36 75 75 win over Alizé Cornet, another player who is having a sizzling summer. The match was a rollercoaster, with Cornet originally leading 63 52, Rybarikova winning nine games in a row to snatch the second set and go up 4-0 in the third, and the whole thing ending after a whopping two hours and 46 minutes.